The present invention relates to a thermal master making device for thermally perforating a thermosensitive stencil to thereby make a master, and a thermal recording device for thermally recording an image on a thermosensitive recording medium. The two devices each includes a thermal head and a platen roller.
A thermal master making device and a thermal recording device have customarily been included in a digital thermal stencil printer and a digital thermal recorder, respectively. The conventional thermal master making device and thermal recording device have the following problems (1)-(3) left unsolved.
(1) Substantial friction acts between a thermosensitive stencil used in the thermal master making device or a thermosensitive recording medium used in the thermal recording device and a platen roller and a thermal head. The resulting static electricity charges the periphery of the platen roller, the surface of the head to contact the stencil or the recording medium, and the surface of the stencil or that of the recording medium. The static electricity is apt to cause the stencil or the recording medium to adhere to and wrap around the platen roller on which a great amount of charge is deposited, thereby obstructing the conveyance of the stencil or the recording medium.
(2) The thermal head includes a resistance layer implementing a plurality of heating elements, and A1 (aluminum) lead electrodes formed on the resistance layer. This kind of thermal head is apt to crack at the stepped edge portions of the lead electrodes. Further, fine impurities are apt to deposit on the lead electrodes and then peeled off, leaving their traces in the form of pin-holes in a protection layer covering the electrodes.
(3) After operation, some potentials are left on the platen roller, stencil or recording medium, and head. Such residual potentials cause the platen roller, stencil or recording medium, cracks and traces of impurities formed in the head, lead electrodes and heating elements to form a current path, so that a small current flows through the current path. The current causes corrosive substances applied to the stencil or the recording medium to turn out corrosive ion products and corrode or oxidize the lead electrodes and heating elements. In the end this obstructs the selective feed of a voltage to the heating elements and prevents the heating elements from generating heat. Images formed in the stencil or on the recording medium in the above condition are partly lost or otherwise defective. Replacing the head which is expensive is a burden on the user and is not desirable from the environment standpoint also.